[Staff/Students] This is the most frequent case, that the user has configured Gmail to access their UPM account. When configuring it, it has told Gmail to "connect to the UPM servers, download the mail and DELETE the messages from the UPM servers". This means that when you access the UPM servers with Webmail you do not find anything.... your UPM email has been downloaded to your Gmail account. To change this behavior you must modify/delete the settings of your Gmail account (Help Gmail functions in other mail accounts) in relation to linking your UPM account.... And we cannot help you with this, as it is an external service and not operated by us. Indicate that from the university's email services we DO NOT recommend the use of Gmail, by doing so you are giving Google your credentials. In addition, you are allowing access and (surely) indexing of your email.

It is advisable to use a regular email client or the Webmail gateway:

UPM Personal Email Configuration
Webmail Personal UPM
UPM Student Email Configuration
UPM Student Webmail